A number of problems occur in the operation of scrag mills of the type in which a log is moved between a pair of circular power saws so as to cut a slab from each side of the log, producing what is called a "log cant". The slabs should be substantially equal in size. Therefore, the log should be centered, as closely as possible, between the saws. Such logs are never perfectly circular in cross section or straight in length, and usually possess a number of other irregularities. As a result, relatively large forces are exerted on the log, as it progresses through the mill, tending to twist it around its longitudinal axis and to move it laterally out of alignment with its desired path between the saws. To the extent that such movements do occur, the log tends to bind against the sides of the rapidly rotating saws, thus generating a great deal of thermal energy which heats the saws to excessively high temperatures. At such temperatures the saw blades warp out of shape giving rise to such vigorous vibrations that it often becomes necessary to stop the mill until the saws have cooled to normal temperatures. If the distortion of the saw blades is sufficiently severe, it may even become necessary to replace them by a fresh pair. The quality of the work may also be impaired. Of course the delays involved are highly objectionable.
Various prior art mechanisms have been devised for setting such logs in position with respect to the saws, usually by a series of knees and for clamping the logs in position by clamping dogs. However, the results still leave much to be desired. The operation is often quite time consuming and the ability of such mechanisms to hold the log in its desired position and path of travel throughout its entire passage through the saws is often insufficient to accomplish the desired degree of perfection. Such deficiencies are particularly marked when logs of different sizes and shapes are to be operated upon by a single mill.
Prior art devices also have been deficient in that the mechanism for moving the log throughout its length between the saws have not exerted enough of a force to eliminate the tendency of some logs to stall between the saws.